The subject invention discloses oxazolidinone derivatives possessing a substituted diazine moiety bonded to an N-aryl ring. The compounds are useful antimicrobial agents, effective against a number of human and veterinary pathogens, including multiply-resistant staphylococci and streptococci, as well as anaerobic organisms such as bacteroides and clostridia species, and acid-fast organisms such as Mycobacterium tuberculosis and Mycobacterium avium. The compounds are particularly useful because they are effective against the latter organisms which are known to be responsible for infection in persons with AIDS.